The invention relates to a parking brake system for a vehicle, including an at least partially bistable valve unit for generating a control pressure for the pilot control of at least one function of the parking brake system, and a relay valve which receives the control pressure from the valve unit and pressurizes or vents at least one spring brake cylinder as a function of the control pressure.
Parking brake systems of the above-described type are very common, particularly in commercial vehicles, where a compressed air-operated parking brake system is often provided to supplement a compressed air-operated service brake. Such parking brake systems usually include a valve unit (potentially having a plurality of individual valves), which may be electrically activated, for example, and generate different control pressures, and a relay valve, which pressurizes or bleeds (vents) the spring brake cylinders as a function of one of the control pressures. In order to facilitate the assembly of all components, all integral parts of the parking brake system are combined in a single sub-assembly, a so-called parking brake module, it being not altogether unusual for reasons of space and efficiency to integrate the parking brake module into the compressed air supply unit.
One disadvantage to such a high degree of integration of the compressed air generation system and the parking brake module is the amount of labor that needs to be expended for repairs in the event of a defect.
The object of the invention, therefore, is to at least partially solve this problem.
This, and other, objects are achieved according to the invention by a parking brake system for a vehicle, including an at least partially bistable valve unit for generating a control pressure for the pilot control of at least one function of the parking brake system, and a relay valve, which receives the control pressure from the valve unit and pressurizes or vents at least one spring brake cylinder as a function of the control pressure. The valve unit is integrated into a first module, which is integrated into a compressed air supply unit, and that the relay valve is arranged in a second module, which is arranged at an interval from the first module and the compressed air supply unit. Separating the parking brake system or, more particularly, the parking brake module into two separate modules, a first module being integrated into the compressed air supply unit and a second module being arranged at an interval from the first module and the compressed air supply unit, ensures easy replacement at least of the second module, which is not integrated into the compressed air supply unit. In this way it is possible, in particular, to replace the relay valve, which is exposed to great stresses, without additional assembly effort.
The first module advantageously includes a trailer control connection, which can be activated by a solenoid valve for performing a test function of a trailer parking brake. To generate a control pressure on the control connection, only a small volume of air is generally needed, for which reason the load acting on the valve generating it is low. An integration into the compressed air supply unit by arranging the relevant solenoid valve in the first module is therefore advantageous.
It is especially preferred if the solenoid valve can be activated with pulse width modulation, in order to provide an anti-jackknife braking function on the trailer control connection. The facility for pulse width-modulated activation allows a continuous pressure modulation on the trailer control connection, affording a graduated braking action of the trailer parking brake. This in turn allows a braking of the vehicle with connected trailer independently of the service brake.
It is also feasible to provide a pressure sensor integrated into the first module for regulating the pressure of a trailer control. The closing of the pressure regulating circuit by a pressure sensor integrated into the first module allows monitoring of the control pressure present on the trailer control connection for little outlay.
In particular, the at least partially bistable valve unit may include a bistable solenoid valve, in order to avoid unwanted closing or opening of the parking brake in the event of a defect. This increases the vehicle safety in general, since a sudden opening of the parking brake system while a vehicle is stationary is excluded in exactly the same way as a sudden closing of the parking brake system while a vehicle is in motion.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.